13.2. Hardening SFTPPlus Deployments¶
The default SFTPPlus configuration provides a balance between a secure deployment, ease of troubleshooting and compatibility with external systems.
This page documents a few steps which can be followed to increase the security of SFTPPlus deployments.
SFTPPlus can operate under a non-privileged account on any operating system. You don't need root or an administrator account to start the SFTPPlus process.
Keep in mind that on Unix-like systems this will not allow SFTPPlus to authenticate accounts from the operating system, you will be limited to only authenticating application-level accounts.
The operating system account used to run the SFTPPlus process only needs the following rights to access SFTPPlus files: * read permissions for the configuration file, * write permissions for the log files, * read/write permissions for the actual files managed by SFTPPlus.
All the files belonging to an SFTPPlus installation should be set so that they only have read permissions for the account under which SFTPPlus runs. They should not have read permissions (or any other permission) for other accounts.
When logs are stored in a local file and log rotation is enabled, SFTPPlus will need write permissions to the log file as well as to the folder containing this file.
If you only send the logs to a syslog server or a remote HTTP server, you will not need write permissions for a local log file.
When using Local Manager, SFTPPlus will need read and write access to its configuration file and to the folder containing this configuration file. This is because SFTPPlus will create a temporary file before updating the main configuration file.
If you don't use Local Manager, you can set SFTPPlus with read-only access to the configuration files.
All SFTPPlus application accounts are locked by default inside their home folder, and there is no configuration option to allow full access.
Accounts belonging to the operating system can be configured in SFTPPlus to have access to all the files found on the machine running SFTPPlus. This includes files from other users, but also files used by the operating system or by other applications.
To reduce the risk of unwanted access to sensitive files, you should always configure an account to be locked inside its home folder.
When you want multiple accounts to access each other's data, design the directory structure so that all files are in a dedicated root folder, and set the home folders for these accounts to this dedicated root folder. By locking the accounts in their home folders, they will still have access to the shared files, but will not have access to the OS files or other files outside of the dedicated common root folder.
By default, SFTPPlus will advertise the product name and version to clients using its file transfer services.
You may conceal the identity of the SFTPPlus file transfer services by configuring a different name or configuring just the name without a version number.
You can do this for the FTP/FTPS service by setting a value for the banner configuration option which starts with the > character.
For the HTTP/HTTPS file transfer service and for the Local Manager service you can use the headers configuration option to set a different value for the standard Server header.
Note that a targeted attacker could still detect the product or even a specific version by observing idiosyncrasies in server operations (for example responses to invalid requests).
For the Local Manager and the HTTPS file transfer services you may configure the service to enable HTTP Strict Transport Security.
This can be done using the headers configuration option.
Note that this will deny the usage of the self-signed certificate generated by default in SFTPPlus.
The easiest way to avoid scan attacks is to use non-standard ports for file transfer services.
When this is not an option, you can configure SFTPPlus to immediately block known usernames widely used by scanners, without forwarding the authentication requests to specialized methods.
You can also configure SFTPPlus to ban an IP once a configured number of failed authentication requests were generated from that source IP in a configured period of time.